KR101162567B1 - Silicon carbide and method of fabricating thereof - Google Patents

Abstract

The present invention relates to silicon carbide and a method for manufacturing the same, and specifically, a polycarbosilane and a silicon nano powder, the amount of residual carbon is low, the crystallinity is high, and the high purity crystalline of polycarbosilane is used more efficiently. It is to provide a method for producing this excellent silicon carbide.

Silicon Carbide, Polycarbosilane, Silicon Nanopowder

Description

Silicon Carbide and Manufacturing Method Thereof {SILICON CARBIDE AND METHOD OF FABRICATING THEREOF}

The present invention relates to silicon carbide and a method of manufacturing the same.

Carbon / silicon carbide (C / SiC) composites and silicon carbide / silicon carbide (SiC / SiC) composites are characterized by high thermal conductivity, excellent corrosion resistance, abrasion resistance, low thermal expansion and light weight, resulting in aerospace parts, automotive disc brakes, next generation engine parts, Research and development is underway for applications in gas turbine components and heat exchangers for cogeneration.

1 is an electron micrograph of a cross section of a typical carbon / silicon carbide (C / SiC) composite. The most commonly used methods for producing such C / SiC composites and SiC / SiC composites include Chemical Vapor Infiltration (CVI) and Polymer Infiltration and Pyrolysis (PIP). have.

Both techniques are based on the general principle of filling the pores between preforms with silicon carbide (SiC) from the decomposition of precursors.

The CVI process deposits high-purity crystalline SiC in the preform, while the PIP is a process in which inorganic polymers such as polysilane, polysiloxane, polycarbosilane and polysilazane are infiltrated and pyrolyzed between the preform and are filled with trace amounts of oxygen and amorphous SiC. .

PIP technology, known as an economically less expensive process, has the disadvantage of producing low purity SiC with lower thermomechanical properties than CVI composites as it has an amorphous glass phase.

The present invention relates to a crystalline silicon carbide having a small amount of carbon remaining using polycarbosilane and silicon nano powder, and a method of manufacturing the same. More specifically, the high purity crystallinity is more efficiently utilized by using the high temperature fluidity of polycarbosilane. It is to provide excellent silicon carbide.

One embodiment of the present invention is to prepare a polycarbosilane solution by mixing polycarbosilane, silicon nanopowder and a solvent (S1); Impregnating the preform into the polycarbosilane solution after the step S1 (S2); An insolubilization step (S3) of thermosetting the impregnated preform after the step S2 for 30 minutes to 1 hour at 150 to 300 ° C; And a calcining step (S4) of heat-treating the preform heat-cured after the step S3 for 1 to 3 hours at 1200 to 1800 ° C .;

Another embodiment of the present invention is a method for producing silicon carbide, wherein the polycarbosilane is polyphenylcarbosilane.

Another embodiment of the present invention is a polyphenylcarbosilane is a method for producing silicon carbide having a weight average molecular weight of 2000 to 6000.

Another embodiment of the present invention is a silicon nano powder is a method for producing silicon carbide having an average particle diameter of 20 to 30nm.

Another embodiment of the present invention is a polycarbosilane solution is a method for producing silicon carbide containing 20 to 50% by weight of polycarbosilane, 5 to 20% by weight of silicon nanopowder and 30 to 75% by weight of a solvent.

Another embodiment of the present invention is to provide a silicon carbide prepared according to the above-described manufacturing method.

Silicon carbide according to the present invention and a method for producing the same by using a polycarbosilane and silicon nanopowder has a small amount of residual carbon and high crystallinity, and has an effect of excellent crystallinity of high purity more efficiently by using high temperature fluidity of polycarbosilane. .

One embodiment of the present invention is to prepare a polycarbosilane solution by mixing polycarbosilane, silicon nanopowder and a solvent (S1); Impregnating the preform into the polycarbosilane solution after the step S1 (S2); An insolubilization step (S3) of thermosetting the impregnated preform after the step S2 for 30 minutes to 1 hour at 150 to 300 ° C; And a calcining step (S4) of heat-treating the preform heat-cured after the step S3 for 1 to 3 hours at 1200 to 1800 ° C .;

First, polycarbosilane, silicon nanopowder and a solvent are mixed to prepare a polycarbosilane solution (S1).

The polycarbosilane may be any one selected from the group consisting of polymethyl carbosilane, polymethylphenyl carbosilane, polyphenyl carbosilane and polyvinyl carbosilane.

Figure 2 schematically shows the structure of a polyphenylcarbosilane according to the present invention. As shown in FIG. 2, the polyphenylcarbosilane has a phenyl group which is silicone-connected by methylene and has excellent thermal stability at the end thereof, and thus is thermally stable up to 400 ° C., and does not change in physical properties or chemical components, and does not have a nucleic acid or a cycle. Soluble in organic solvents such as nucleic acid, toluene, tetrahydrofuran, benzene, chloroform, etc., and can be used as a polymer impregnation and pyrolysis material.

It does not specifically limit as a precursor of the said polyphenyl carbosilane, For example, it can manufacture using phenyl trichlorosilane, diphenyl dichlorosilane, polydimethylsilane, polymethylphenylsilane, etc. Among them, polymethyl phenyl silane may be preferably used, and the method for preparing polyphenyl carbosilane may be arbitrarily selected from methods well known in the art to which the present invention pertains, and Korean Patent No. 10-2006- The following description is made with reference to 17755.

First, polymethylphenylsilane is produced by condensation reaction of phenylmethyldichlorosilane with an alkali metal, preferably sodium metal, under an inert atmosphere such as nitrogen.

Specifically, in an inert atmosphere, the sodium metal is finely chopped in a solvent such as xylene, tetrahydrofuran (THF), toluene, and the like, followed by heating and stirring to disperse the sodium metal completely, where phenylmethyl Dichlorosilane can be prepared by injecting and heating to form a polymer and then removing residual metal sodium and solvent.

The prepared polymethylphenylsilane may be converted to polyphenylcarbosilane using a high temperature pressurized reactor. The conversion reaction temperature is preferably 300 to 350 ° C, and polyphenylcarbosilane having a molecular weight suitable for coating can be prepared by polymerization at 400 to 450 ° C.

The polyphenyl carbosilane preferably has a weight average molecular weight of 2000 to 6000, more preferably 2500 to 4000. The larger the molecular weight of the polyphenyl carbosilane, the higher the ceramic yield can be obtained after heat treatment. However, if the molecular weight exceeds 6000, the polyphenyl carbosilane may not be completely dissolved in an organic solvent such as nucleic acid. When the molecular weight of the polyphenylcarbosilane is less than 2000, the ceramic yield is low, so that it takes a long time to increase the density of the composite.

The silicon nano powder preferably has an average particle diameter of 20 to 30 nm.

The silicon nano powder has the advantage of being well dispersed in the polyphenyl carbosilane solution when it is in the above range.

In addition, in the present invention, silicon is used in the form of nanopowder, and since the surface area is large, it may have an advantage of easily reacting with the remaining carbon and converting it into silicon carbide.

The solvent is not particularly limited as an organic solvent, and examples thereof include nucleic acid, cyclonucleic acid, tetrahydrofuran and benzene.

The polycarbosilane, the silicon nanopowder, and the solvent described above are mixed in a conventional manner to prepare a polycarbosilane solution.

The polycarbosilane solution comprises 20 to 50% by weight of polycarbosilane, 5 to 20% by weight of silicon nanopowder, preferably 5 to 10% by weight and 30 to 75% by weight of solvent.

When the content of the polycarbosilane is within the above range, there is an advantage that it is easy to penetrate the preform having good fluidity.

When the content of the silicon nano powder is in the above range there is an advantage that it is well dispersed in a polyphenyl carbosilane solution. In particular, when the content of the silicon nano powder exceeds 20% by weight, there is a problem that the silicon nano powder is precipitated without being dispersed in the polyphenylcarbosilane solution.

When the content of the solvent is within the above range there is an advantage that can be prepared a good fluidity solution.

Subsequently, impregnating the preform into the polycarbosilane solution is performed (S2).

The preform may include a carbon preform or a silicon carbide preform, but is not limited thereto.

The impregnation process may be carried out according to a conventional method well known in the art. After the step S2 is carried out an insolubilization step of thermosetting the impregnated preform for 30 minutes to 1 hour at 150 to 300 ℃, preferably 150 to 200 ℃ (S3).

In this case, the insolubilization step is preferable in that it can be insolubilized by forming an Si—O—Si bond because it is easily reacted with oxygen.

When the temperature range is within the above range, the polyphenylcarbosilane has the advantage of being the minimum temperature that can be cured, and when the thermosetting is carried out within the time range, the polyphenylcarbosilane has the advantage of being the minimum time that can be cured.

After the step S3 is performed a baking step of heat-treating the heat-cured preform for 1 to 3 hours at 1200 to 1800 ℃ (S4).

The sintering step serves to convert the remaining carbon into crystalline silicon carbide by reacting with the silicon nanopowder, and has the advantage of converting the crystalline silicon carbide to heat treatment conditions to a minimum when the process conditions are performed at the temperature and time.

According to another embodiment of the present invention, to provide a silicon carbide prepared according to the above-described manufacturing method.

The silicon carbide preferably has an element content (at%) ratio of silicon atoms to carbon atoms of 1: 1 to 1.3.

The silicon carbide has the advantage that the high temperature oxidation resistance is enhanced when the element content (at%) ratio of silicon atoms to carbon atoms is within the above range. Specifically, the present invention uses silicon nanopowder, which has the above range because it removes residual carbon undergoing oxidation at less than 400 ^° C. and generates only crystalline silicon carbide having excellent oxidation resistance. As a result, high temperature oxidation resistance can be obtained.

Hereinafter, preferred examples and comparative examples of the present invention will be described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

Example  One

30g of polyphenylcarbosilane having a weight average molecular weight of 3,000 was dissolved in 100g of cyclonucleic acid to prepare a polyphenylcarbosilane solution.

Into the prepared polyphenyl carbosilane solution 10g of silicon nanopowder having a size of 30nm was added and well dispersed. The surface of the carbon preform having a size of 30 mm × 30 mm × 10 mm to be impregnated was washed with ethanol and dried at 80 ° C. for 30 minutes. It was impregnated in 100cc of polyphenylcarbosilane solution in which the silicon nanopowder was dispersed using a dip coater for 5 minutes, the sample was pulled up to 1 mm / sec, and then thermally cured in air at 150 ° C. for 30 minutes, and then at 1400 ° C. under argon atmosphere. Heat treatment was performed for 60 minutes at to obtain a silicon carbide matrix with excellent crystallinity. This process was repeated five times to obtain a densely packed C / SiC composite.

Example  2

30 g of polyphenyl carbosilane having a weight average molecular weight of 3,000 was dissolved in 100 g of cyclonucleic acid to prepare a polyphenyl carbosilane solution.

10 g of the silicon nanopowder having a size of 30 nm was added to the prepared polyphenylcarbosilane solution and well dispersed. The surface of the carbon preform having a size of 30 mm × 30 mm × 10 mm to be impregnated was washed with ethanol and dried at 80 ° C. for 30 minutes. It was impregnated in 100cc of polyphenylcarbosilane solution in which the silicon nanopowder was dispersed using a dip coater for 5 minutes, the sample was pulled up to 1 mm / sec, and then thermally cured in air at 150 ° C. for 30 minutes, and then at 1400 ° C. under argon atmosphere. Heat treatment was performed for 60 minutes at to obtain a silicon carbide matrix with excellent crystallinity. This process was repeated 10 times to obtain a densely packed C / SiC composite.

Comparative example  One

30 g of polyphenyl carbosilane having a weight average molecular weight of 3,000 was dissolved in 100 g of cyclonucleic acid to prepare a polyphenyl carbosilane solution. The surface of the carbon preform having a size of 30 mm × 30 mm × 10 mm to be impregnated was washed with ethanol and dried at 80 ° C. for 30 minutes. The polyphenylcarbosilane solution was impregnated with 100cc of the polyphenylcarbosilane solution for 5 minutes using a dip coater, and the sample was pulled up to 1 mm / sec, and then thermally cured in air at 150 ° C. for 30 minutes, and heat-treated at 1400 ° C. for 60 minutes in an argon atmosphere. Carbon and partially crystallized silicon carbide matrix phase were obtained. This process was repeated five times, but the C / SiC composite having a filling rate of less than 70% was obtained.

Property evaluation

3 is a transmission electron micrograph of the silicon carbide matrix phase prepared according to Example 1 of the present invention. As shown in FIG. 3, it was confirmed that a silicon carbide matrix phase having excellent crystallinity was obtained when heat-cured after impregnation using a polycarbosilane and silicon nanopowder mixed solution and heat-treated at 1400 ° C. for 60 minutes in an argon atmosphere.

4 is a transmission electron micrograph of the silicon carbide matrix phase prepared according to Comparative Example 1. As shown in FIG. 4, the silicon carbide nanocrystals were formed when heat-cured after impregnation using only a polycarbosilane solution and heat-treated at 1400 ° C. for 60 minutes in an argon atmosphere, but most of them obtained amorphous SiC matrix.

5 is an energy dispersive spectroscopy (EDS) analysis of the silicon carbide matrix phase prepared according to Example 1 of the present invention. As shown in Figure 5 as a result of the component analysis with EDS it was confirmed that the SiC is made quantitative element ratio (at%) of silicon atoms to carbon atoms of about 1: 1.2.

6 is an EDS analysis result of measuring a silicon carbide matrix phase prepared according to Comparative Example 1. FIG. As shown in FIG. 6, when the component analysis was performed with EDS, it was found that an excessive carbon content was present in an element ratio (at%) of silicon atoms to carbon atoms of about 1: 3.3.

As a result of the physical property evaluation, it can be seen that the matrix phase of the C / SiC composite prepared with the polyphenylcarbosilane solution in which the silicon nanopowder prepared in Example 1 of the present invention is dispersed shows excellent crystallinity, and the polyphenylcarbosilane solution It can be seen that the material exhibits higher crystallinity than that of Comparative Example 1 using only oxidized resistance and abrasion resistance. Generally, crystalline silicon carbide / silicon carbide (SiC / SiC) composites have aerospace components, automotive disc brakes, next-generation engine components, gas turbine components for cogeneration, due to their high thermal conductivity, excellent corrosion resistance, low thermal expansion and light weight. Research and development is in progress for applications such as heat exchangers.

All simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

1 is an electron micrograph of a cross section of a typical carbon / silicon carbide (C / SiC) composite.

Figure 2 schematically shows the structure of a polyphenylcarbosilane according to the present invention.

3 is a transmission electron micrograph of the silicon carbide matrix phase prepared according to Example 1 of the present invention.

4 is a transmission electron micrograph of the silicon carbide matrix phase prepared according to Comparative Example 1.

5 is an energy dispersive spectroscopy (EDS) analysis of the silicon carbide matrix phase prepared according to Example 1 of the present invention.

6 is an EDS analysis result of measuring a silicon carbide matrix phase prepared according to Comparative Example 1. FIG.

Claims (7)

Preparing a polycarbosilane solution by mixing polycarbosilane, a silicon nanopowder having an average particle diameter of 20 to 30 nm, and a solvent (S1); Impregnating the preform into the polycarbosilane solution after the step S1 (S2); An insolubilization step (S3) of thermosetting the impregnated preform after the step S2 for 30 minutes to 1 hour at 150 to 300 ° C; And And a calcining step (S4) of heat-treating the heat-formed preform at 1200 to 1800 ° C. for 1 to 3 hours after the step S3. The polycarbosilane solution comprises 20 to 50% by weight of polycarbosilane, 5 to 20% by weight of silicon nanopowder and 30 to 75% by weight of a solvent. The method of claim 1, wherein the polycarbosilane is polyphenylcarbosilane. The method of claim 2, wherein the polyphenyl carbosilane has a weight average molecular weight of 2000 to 6000. delete delete Silicon carbide prepared according to any one of claims 1 to 3. 7. The silicon carbide according to claim 6, wherein the silicon carbide has an element content (at%) ratio of silicon atoms to carbon atoms of 1: 1 to 1.3.

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